wid9et
Sign In

Water Intake Calculator

Estimate how much water to drink each day based on your weight and exercise.

Based on what you entered, aim for around 2.3 L-2.9 L of water across the day.

Water based on your weight

2.1 L-2.5 L

Your estimated daily amount before adding exercise.

Extra water for exercise

200 ml-400 ml

Extra water you may need while exercising.

Estimated total per day

2.3 L-2.9 L

2,300 ml-2,850 ml

Your estimated total for the whole day.

About this many glasses

9-11

Based on a 250 ml glass.

Explore more Health & Fitness →Build your own widget - free →

How to use the Water Intake Calculator

  1. 1Choose kilograms or pounds and enter your body weight.
  2. 2Enter the number of minutes of exercise you expect on a typical day, or enter zero for a baseline-only estimate.
  3. 3Use the result as a broad planning range and adjust for thirst, weather, sweat rate, food and professional advice where relevant.

Useful tips

  • •Fluid comes from more than plain water. Other drinks and water in food can contribute to total daily intake.
  • •Hot weather, prolonged exercise, fever, vomiting or diarrhoea can increase fluid needs, while some medical conditions require limits.
  • •For long or sweaty exercise, your own sweat rate is more useful than a generic exercise allowance.

Frequently asked questions

How is the baseline range calculated?

The calculator uses 30-35 ml of total fluid per kilogram of body weight as a broad planning range. That weight-based figure is used in NICE nutrition-support guidance, so it should not be treated as a personalised drinking prescription for every healthy adult.

How is the exercise allowance calculated?

The calculator shows a broad 0.4-0.8 litres per hour range for exercise and scales it to the minutes entered. Actual sweat loss varies greatly with body size, intensity, clothing, fitness and temperature, so longer or hotter sessions are better guided by your own measured sweat rate.

How does this compare with the NHS 6-8 glasses guidance?

The NHS advises most people to aim for about 6-8 cups or glasses of fluid a day as a general guide, with more often needed during hot weather, prolonged physical activity, pregnancy, breastfeeding or illness. The weight-based calculator is another planning estimate rather than a replacement for that guidance.

Can drinking too much water be harmful?

Yes. Excessive intake can dilute blood sodium and cause hyponatraemia. Do not force large amounts of water beyond thirst or professional advice, particularly during endurance exercise.

Who should get personalised hydration advice?

People with kidney or heart disease, fluid restrictions, pregnancy or breastfeeding, significant illness, or medicines that affect fluid balance should follow advice from a qualified health professional rather than a generic calculator.

Does Wid9et store my weight or exercise data?

No. This calculator runs locally in your browser and does not upload the values entered into the tool.